A likely candidate is that ports on the Mac are not accessible; I'm not familiar enough with how things work, but I think the overall strategy would be to identify open ports and use these via options(ports=123).

Not sure if this is relevant but this is what I get (regardless of the port). Although may be this is what is supposed to be since there is no process communicating to the 11709 port. Anyway, BiocParallel:::.bpmakeForkCluster is not cooperating with me today.

The 'SOCK' class of the return value is a red herring here. A simple fork isn't rich enough to support the BiocParallel behavior, which requires communication between the forked and master process. Sockets are used for that communication.

Sorry for the delay and thanks for debugging. I can sort of guess at the issue and have provided a patched version in BiocParallel 1.8.1 (current Bioc release version 3.4) and 1.9.1 (bioc devel), available with either

or after the next build (likely Sunday afternoon, eastern time) via biocLite("BiocParallel").

The workaround lets you set the host using a global option

options(bphost="localhost")

instead of the default Sys.info()[["nodename"]]. Set the option any time before calling bplapply(), bpvec(), or bpstart(). I'd appreciate hearing whether this works for you (and others), and if so will make a more permanent change.